Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session H58: Emulsions and Foams |
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Sponsoring Units: GSOFT Chair: Rodrigo Guerra, New York University Room: BCEC 257A |
Tuesday, March 5, 2019 2:30PM - 2:42PM |
H58.00001: Faceted liquid droplets: when colloids are attracted by topological defects Shir Liber, Alexander V. Butenko, Eli Sloutskin Particles at disordered droplet interfaces were extensively investigated, aiming both at their fundamental physics and at their applications in particle-stabilized pharmaceuticals and aerosols. Yet, particles residing at the ubiquitous ordered interfaces have never been studied. |
Tuesday, March 5, 2019 2:42PM - 2:54PM |
H58.00002: Adsorption of Anionic Nanoparticles at Oil-water Interfaces Driven by Ion Partitioning Robert Keane, Wei Hong, Wei He, Robbie Bancroft, Sam Teale, Anthony Dinsmore Adsorption of particles at oil-water interfaces is the basis of Pickering emulsions, which are common in nature and industry. For anionic particles, however, the negative potential at the water-oil interface inhibits spontaneous adsorption, which limits the scope of useful materials. Here we address this problem by adding ions that selectively partition in the two phases, thereby changing the interfacial potential and driving anionic particle adsorption. We add oil-soluble tetrabutyl ammonium perchlorate (TBAP) to the nonpolar phase and Ludox silica nanoparticles to the aqueous phase. We find a threshold TBAP concentration, above which emulsions are stable for months. This threshold increases with particle concentration and with the oil’s dielectric constant. Adding salt to the water raises the threshold and causes spontaneous coalescence. The results are consistent with a model based on Poisson-Boltzmann theory, which predicts that TBAP anions (ClO4-) migrate into the water phase and leave behind a net positive charge in the oil. Our results clarify the role of interfacial electrostatics and show how a large class of inorganic anionic nanoparticles can be used to stabilize emulsions. |
Tuesday, March 5, 2019 2:54PM - 3:06PM |
H58.00003: Domain, nanoridge and mesa growth kinetics in stratifying foam films Vivek Sharma, Yiran Zhang, Subinuer Yilixiati, Chrystian Ochoa, Chenxian Xu Ultrathin films exhibit stratification due to confinement-induced structuring and layering of small molecules in simple fluids, and of supramolecular structures like micelles, lipid layers and nanoparticles in complex fluids. Stratification proceeds by the formation and growth of thinner domains at the expense of surrounding thicker film, and results in formation of nanoscopic terraces and mesas within a film. The detailed mechanisms underlying stratification are still under debate, and are resolved in this contribution by addressing long-standing experimental and theoretical challenges. Thickness variations in stratifying films are visualized and analyzed using interferometry, digital imaging and optical microscopy (IDIOM) protocols, with unprecedented high spatial (thickness < 100 nm, lateral ~500 nm) and temporal resolution (< 1 ms). Using IDIOM protocols we developed recently, we characterize the shape and the growth dynamics of nanoridges and mesas that flank the expanding domains in micellar thin films. We show that topographical changes including nanoridge & mesa growth, and the overall stratification dynamics, can be described quantitatively by nonlinear thin film equation, amended with supramolecular oscillatory surface forces. |
Tuesday, March 5, 2019 3:06PM - 3:18PM |
H58.00004: Iridescent clusters and marginal regeneration in vertical soap films Erica Li, Chenxian Xu, Elizabeth John, Chrystian Ochoa, Vivek Sharma
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Tuesday, March 5, 2019 3:18PM - 3:30PM |
H58.00005: Stepwise Thinning and Nanoscopic Thickness Variations in Foam Films Formed by Aqueous Sodium Naphthenate Solutions Chrystian Ochoa, Shang Gao, Samanvaya Srivastava, Vivek Sharma Sodium Naphthenates found in crude oils can act as surfactants and self-assemble in aqueous solutions to form micelles and liquid crystals. Understanding and controlling the drainage kinetics of thin films is an important problem that underlies the stability, lifetime and rheology of petroleum foams and emulsions. Here, we show that foam films formed by aqueous solutions of sodium naphthenates exhibit step-wise thinning or stratification, due to the influence of non-DLVO forces, including supramolecular oscillatory structural forces. We utilize Interferometry, Digital, Imaging, Optical Microscopy protocols, previously developed by our group, to investigate the drainage and stratification in micellar foam films (< 100 nm) with high spatial (thickness < 10 nm) and temporal resolution (< 1 ms). We determine how the concentration of added sodium naphthenates influences the nanoscopic topography, stratification kinetics and step size of foam films, and contrast the results with behavior observed with stratifying foams made with sodium dodecyl sulfate (SDS) solutions. We span a relatively wide concentration range, such that micelle shape and size vary, as is revealed by complementary small angle x-ray scattering experiments. |
Tuesday, March 5, 2019 3:30PM - 3:42PM |
H58.00006: Phase behavior and structure of sodium napthenate micelles Shang Gao, Chrystian Ochoa, Vivek Sharma, Samanvaya Srivastava The formation and stability of petroleum foams and emulsions can sometimes be attributed to sodium naphthenates surfactants. However, relatively little information is available about the sizes and shapes of self-assembled structures formed by sodium naphthenates, limiting our ability to control foam or emulsion stability and the success of sequestration or extraction processes. In this study, we develop a comprehensive understanding of the phase behavior of sodium naphthenate micelles (including size, shape and inter-micellar interactions) through a combination of static and dynamic scattering measurements. Small-angle X-ray scattering (SAXS) measurements revealed intriguing trends – micelle shape and size varied with increasing surfactant concentrations in the dilute (<5 wt%) limit. At higher concentrations (5 wt% – 40 wt%), while the micelle shapes and sizes remained largely invariant, inter-micellar interactions became increasingly significant, leading to stronger structure factor contributions to scattering intensities. These concentration-dependent trends are contrasted against trends in hydrodynamic size and zeta-potential of the micelles from dynamic light scattering measurements, as well as stratification kinetics of foams containing sodium naphthenate micelles. |
Tuesday, March 5, 2019 3:42PM - 3:54PM |
H58.00007: Rheology and structure of macro- and nano-emulsions with adhesive droplets Neda Sanatkaran, Reza Foudazi In this work, we investigate the viscoelastic and flow properties of oil-in-water nanoemulsions to verify rheological scaling models of macroemulsion systems. Emulsions were prepared using silicone oil with different average droplet sizes (ranging from 1 µm to below 100 nm) dispersed in sodium dodecyl sulfate solution above the critical micelle concentration. Droplet size distributions were narrow and remained unchanged for all the samples. Viscoelastic responses and yielding of emulsions were examined as a function of dispersed phase volume fractions (35 – 65 %) for each of the droplet sizes. The range of volume fractions for the samples was obtained via an evaporation-dilution technique. We elucidate the experimental result using the theoretical models for interdroplet interactions. The scaling of rheological properties with Laplace pressures becomes invalid in the nanoemulsion regime. The liquid, gel, and glass states are investigated based on the elastic modulus, yield stress and yield strain of studied adhesive emulsions. |
Tuesday, March 5, 2019 3:54PM - 4:06PM |
H58.00008: Formation, growth and coalescence of nanoscopic mesas in stratifying foam films Chenxian Xu, Subinuer Yilixiati, Yiran Zhang, Vivek Sharma Ultrathin micellar foam films exhibit stratification due to confinement-induced structuring and layering of micelles. Stratification proceeds by the formation and growth of thinner domains at the expense of surrounding thicker film, and flows and instabilities drive the formation of nanoscopic terraces, ridges and mesas within a film. The detailed mechanisms underlying stratification are still under debate, and are resolved in this contribution by addressing long-standing experimental and theoretical challenges. Thickness variations in stratifying films are visualized and analyzed using interferometry, digital imaging and optical microscopy (IDIOM) protocols, with unprecedented high spatial (thickness < 100 nm, lateral ~500 nm) and temporal resolution (< 1 ms). Using IDIOM protocols we developed recently, we characterize the shape and the growth dynamics of mesas that flank the expanding domains in micellar thin films, and we track their evolution, as well as coalescence dynamics. |
Tuesday, March 5, 2019 4:06PM - 4:18PM |
H58.00009: Foam formation analysis during drainage of a surfactant solution Nicolle De Lima, Shima Parsa, Marcio Carvalho Foam is widely used in oil recovery operations to maximize oil production, and solve problems caused by either a thief zone or gravity override. Foam, that can be pre-formed and injected in the reservoir or produced in-situ through the pore space, fills the high permeability areas known as thief zones and divert the displacing fluid into the direction of trapped oil, reducing the relative permeability of gas and leading to a more stable flood front. The presence of liquid lamellae between gas bubbles in the foam also reduces the gas mobility, by the increase of the gas apparent viscosity. The flow mobility is a function of the pore geometry and foam properties. However, the dynamics of foam in a porous media is not fully understood due to its complexity. The goal of this research is to study foam formation during drainage of a two-dimensional porous media glass model by visualizing the pore scale displacement flow of a surfactant solution by injected gas. A microfluidic setup composed of glass micromodel, syringe pump, pressure transducer, and a microscope is used to study the evolution of the phase distribution and foam characteristics as a function of pore space geometry and flow conditions through image processing. |
Tuesday, March 5, 2019 4:18PM - 4:30PM |
H58.00010: Capillary imbibition of emulsions in thin rectangular channels Masoud Norouzi Darabad, Samira Abedi, Siva A Vanapalli, Mark W Vaughn Emulsions imbibing in a capillary under transient surface-tension driven flow display an unexpected richness in droplet interactions, clustering and ordering. Droplet size and concentration effects on the droplet interactions of monodisperse oil-in-water emulsions are demonstrated by use of a thin channel to form a pseudo 2-dimensional flow. We categorize droplet-droplet and cluster-cluster interactions at the microscale and find markedly different behavior in ordering, relative phase velocity and droplet-induced interface perturbation depending on concentration and the relative size of the droplets compared to the channel height. |
Tuesday, March 5, 2019 4:30PM - 4:42PM |
H58.00011: Spinning and chaining emulsion droplets in ultrasonic standing waves Mohammed Abdelaziz, Jairo A Diaz, David Grier, Mauricio Hoyos We demonstrate experimentally that emulsion droplets of TPM (3-(trimethoxysilyl)propyl methacrylate) in water spin when levitated in ultrasound, and that the spinning droplets organize themselves into long spinning chains. When the same droplets are solidified into spheres by free-radical polymerization, they no longer spin, and they form crystals rather than chains. We explain these acoustokinetic phenomena through a dipole-order expansion of the incident and scattered waves, by analogy to the theory of optical trapping. |
Tuesday, March 5, 2019 4:42PM - 4:54PM |
H58.00012: Molecular Dynamics Simulations of Liquid-Liquid Phase Separation in Biology Ian Seim, Amy Gladfelter, Daphne Klotsa A newly appreciated mechanism by which biochemistry is organized in cells without membrane barriers is liquid-liquid phase separation (LLPS). RNA and protein condense into liquid droplets through LLPS and are crucial for normal physiological function, but they are also implicated in the development of several neurological diseases as well as theories about the origins of life and cells themselves. Since the means by which droplets form, maintain shape, and achieve molecular specificity are poorly understood, a major challenge is to understand how nanometer scale molecules coalesce to produce cellular bodies of diverse material properties and distinct identities. Our aim is to model the process and properties of LLPS involving mRNAs and disordered proteins using molecular dynamics (MD). Specifically, by using both low and high-resolution representations of the system, we can map sequence-specific effects onto a low-resolution setting. In the coarse-grained space, the solvent is modeled implicitly using Brownian dynamics and the molecules as bead-spring polymers. These techniques provide access to space and time-scales that are critical to the phase separated state which involves the collective behavior of thousands of molecules. |
Tuesday, March 5, 2019 4:54PM - 5:06PM |
H58.00013: Measuring the non-equilibrium fluctuations of biological liquid-liquid phase separation Sebastian Coupe, Nikta Fakhri In biological systems, liquid-liquid phase separation (LLPS) is used to facilitate biochemical reactions, provide cellular compartmentalization, and sequester condition-specific factors. Whether biological LLPS events are active processes remains a difficult question to address because experiments that alter cellular ATP levels also affect the liquid properties of LLPS states. Understanding when different biological LLPS phenomena are active will provide insight into how the cell controls and drives their formation. The first instance of biological LLPS defined and one of the best characterized is the P granule of C. elegans. P granules exist in the cytosol of C. elegans germ-line cells and specify polarity during early embryonic development. To detect active processes in P granules, we measure irreversibility in the positional trajectories of single-walled carbon nanotube probes targeted to the P granules of C. elegans embryos. These extremely bright, photostable, infrared fluorophores provide sufficiently long single-particle trajectories for irreversibility calculations. By measuring irreversibility in the fluctuations of P granules we hope to understand if and when P granules are active liquid states and to directly connect this to a cellular chemical energy input. |
Tuesday, March 5, 2019 5:06PM - 5:18PM |
H58.00014: Self-swallowing Droplets Luoran Shang, Alireza Abbaspourrad, Yuanjin Zhao, David A Weitz Microdroplets attract huge interest as it provides prototype for many industrial and biological systems such as emulsions, porous media, and blood-flow. Specifically, controlling droplets shape is crucial for both fundamental and practical values. Here, we report a novel self-swallowing droplet behavior in a microfluidic channel. It arises when water droplet moves through a partially miscible oil containing large amount of colloidal particles. The rapid mass transfer causes reduction of interfacial area, which leads to particles jamming and phase transition. As a result, an elastic film is generated and soon undergoes a buckling instability in response to the compressive stress due to volume shrinkage of the droplets. Therefore, a re-entrant cavity forms at the rear interface through which a jet of the outer fluid penetrates the droplet. The degree of the swallowing behavior and thus the shape of the droplets could be well adjusted by changing the experimental parameters, and the whole swallowing process could be reversibly regulated. This work not only provides indications for intriguing fundamental questions concerning hydrodynamic and interfacial effects, but also inspires technical innovations including in microfluidics, printing, soft materials processing, etc. |
Tuesday, March 5, 2019 5:18PM - 5:30PM |
H58.00015: In situ wrinkling during evaporative drying of a polymer solution drop on a soft swellable substrate Sumita Sahoo, Rabibrata Mukherjee A sessile liquid drop can deform the substrate on which it rests if the solid is sufficiently “soft” because of the capillary forces exerted by the drop. The drying of complex fluids such as polymer solution involves complex spatiotemporal evolution which involves solvent diffusion, glass transition etc. We have studied here evaporative drying of a polymethylmethacrylate (PMMA) in tetrahydrofuran (THF) solution drop on a soft PDMS substrate. We have observed two distinct type of wrinkles depending on the initial polymer concentration, such as radial lines and central depression with concentric rings A thin polymeric skin at air-polymer interface of the drop is formed due to fast evaporation as well as fast diffusion of THF into the substrate, which gets wrinkled with gradual decrease in the solution volume enclosed by it. |
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